Ah! The One I Yearn for Is a White-Winged Angel!

Skuld admires Belldandy's angel and wants to have one as well. Skuld tries training her skills with inventions. Then something ouside threatens the girls and it's up to Urd to summon her angel, but it's revealed that Urd can't because she told her angel earlier to never come out ever again. What will the goddesses do?